There has been a Coral mystery that has perplexed scientists for a while. The mystery – missing ocean microplastic, where 70% of the plastic litter that entered the oceans vanished without a trace. The latest study at Kyushu University might supply an answer to this enigma.
Researchers from Japan and Thailand investigated the adhesion and accumulation of microplastics in four coral species; Lobophyllia sp. Platygyra sinensis, Pocillopora cf. damicornis, and Porites lutea. The study found microplastic contamination in all three distinct components of coral anatomy – surface mucus, tissue, and skeleton. Researchers indicate that corals may act as a ‘sink’ for microplastics by absorbing them from the oceans.
The study found several potential pathways for microplastic accumulation; 1) adhesion on coral surface, 2) accumulation in coral tissue, or 3) deposition in the skeleton. Among the studied species from the Gulf of Thailand, P. cf. damicornis exhibited the highest degree of accumulation. While the studies Rades et al. (2024) and Mouchi et al. (2019) reported no negative impact on corals, even after a long period of exposure, other studies demonstrate the adverse effect on mucus production, photosynthetic efficiency, and growth rates of corals.
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Microplastics in Corals
“Coral has three main anatomical parts: the surface mucus, the outside of the coral body; the tissue, which is the inner parts of the coral; and the skeleton, the hard deposits of calcium carbonate they produce. Our first step was to develop a way to extract and identify microplastics from our coral samples,” says Jandang.
“We put our samples through a series of simple chemical washes designed to break apart each anatomical layer. After each subsequent layer was dissolved, we would filter out the content and then work on the next layer.”, Jandang continues.
The team collected and studied 27 coral samples across the four species, and found 174 microplastics ranging 101–200 μm in size. Of these, 38% of microplastics were detected on the surface mucus, 25% in the tissue, and 37% were seen in the skeleton. Nylon, polyacetylene, and polyethylene terephthalate (PET) were the most prevalent microplastics.
As coral reefs are ecosystems with profound biological significance, serving as crucial habitats for diverse marine species, plastic pollution in corals may have a catastrophic impact on the overall environment. We have very little idea about the capacity of corals for the temporary or permanent uptake of microplastics from reef ecosystems.
“We also do not know the health effects of microplastics on coral and the larger reef community. There is still much to be done to accurately evaluate the impact of microplastics on our ecosystem,” said Professor Isobe.
As coral skeletons are intact after dying, the finding finds that the ingested microplastic is preserved in them for hundreds of years, indicating that the corals act as a ‘sink’ for the microplastics.
“The ‘missing plastic problem’ has been troubling scientists who track marine plastic waste, but this evidence suggests that corals could account for that missing plastic,” says Jandang. “Since coral skeletons remain intact after they die, these deposited microplastics can potentially be preserved for hundreds of years. Similar to mosquitos in amber.”
Journal Reference:
Jandang, S., Alfonso, M. B., Nakano, H., Phinchan, N., Darumas, U., Viyakarn, V., Chavanich, S., & Isobe, A. (2024). Possible sink of missing ocean plastic: Accumulation patterns in reef-building corals in the Gulf of Thailand. Science of The Total Environment, 954, 176210. DOI: 10.1016/j.scitotenv.2024.176210